Prototype Space Sensors Take Test Ride on NASA ER-2

Scientists
recently completed test flights with prototypes of potential satellite sensors
- including two from NASA's Jet Propulsion Laboratory in Pasadena, California
-- over the Western United States, probing basic science questions about
aerosols, clouds, air quality and global ocean ecosystems.

The flight
campaign, called Aerosol Characterization from Polarimeter and Lidar (ACEPOL),
sought to test capabilities of several proposed instruments for the Aerosol-Cloud-Ecosystem
(ACE) pre-formulation
study.

Aerosols are
small solid or liquid particles suspended in Earth's atmosphere, like fine
dust, smoke, pollen or soot. These particles scatter and absorb sunlight and
are critical to the formation of clouds and precipitation. Scientists can analyze
this scattered light using instruments like polarimeters, which measure the
color and polarization of the scattered light, and lidars, which use lasers to
probe the atmosphere. Together these data sets provide key information about
aerosol properties, including size, shape and chemical composition --
information that provides a better understanding and assessment of their
effects on weather, climate and air quality.

Prior to being
launched into space, airborne versions of satellite sensors typically take a
test ride on NASA's ER-2 high-altitude aircraft. The platform, based at NASA's
Armstrong Flight Research Center in Palmdale, California, flies at altitudes of
up to 70,000 feet (21,336 meters), and provides a vantage point and conditions
similar to space. By flying these instruments on an aircraft before the expense
of launching them into space, scientists and engineers can make adjustments to
the hardware and data retrieval algorithms.

The ER-2 also
enables scientists to observe specific events of interest, like wildfires or
volcanic eruptions, to gain a more comprehensive collection of different types
of aerosols in different conditions. The aircraft test phase in sensor
development is helpful for ensuring instruments are collecting both accurate
and useful data prior to the time the final version of the sensors makes its
trip into space.

In addition to
testing capabilities of new sensors, ACEPOL flights also provided calibration
and evaluation data for NASA's Cloud-Aerosol Lidar and Infrared Pathfinder
Satellite Observation (CALIPSO) satellite lidar by staging satellite
underpasses as part of their flight plans. In addition to comparisons with
CALIPSO, ACEPOL also contributes to the development of future satellite
missions, including the European Space Agency's EarthCare, the European Organization for the
Exploitation of Meteorological Satellites' Meteorological Operational Satellite
- Second Generation (METOP-SG), and NASA's Multi-Angle Imager for
Aerosols (MAIA) and Plankton, Aerosol, Cloud,
ocean Ecosystem (PACE) programs. MAIA is being built and is managed by JPL.

The team
completed nine flights that wrapped up in mid-November, observing targets such
as California's Central Valley and the Pacific Ocean, and as far east as Arizona,
where the team observed smoke from controlled forest fires near Flagstaff.

The ER-2's
payload included four airborne polarimeters -- Airborne Hyper-Angular Rainbow
Polarimeter (AirHARP), JPL's
Airborne Multi-angle SpectroPolarimetric Imager (AirMSPI), Airborne Spectropolarimeter for
Planetary Exploration (AirSPEX) and Research Scanning Polarimeter
(RSP) -- and two lidar instruments - Cloud
Physics Lidar (CPL) and High Spectral Resolution Lidar-2 (HSRL-2). Each of the polarimeters used different techniques and
angles to measure and record data. The instruments also differed from one
another in size and power. From an engineering perspective, the ultimate goal
of the ACEPOL mission was to better understand how those overall differences
translate into data collection.

The combination
of the polarimeter and lidar instruments, along with ground-based data from
stationary air quality measurement stations, provide scientists with a more complete picture of the
three-dimensional distribution of aerosols in Earth's atmosphere. Using a
variety of different approaches for collecting data also enables scientists to
differentiate between various types of aerosols (e.g., smoke, dust, pollution)
and clouds (cirrus, stratus, etc.).

The ACEPOL
mission involved partnership between multiple NASA centers, including Langley
Research Center in Hampton, Virginia; Goddard Space Flight Center in Greenbelt,
Maryland; the Goddard Institute for Space Studies in New York City; and JPL. The
mission also included international partnership with the Netherlands Institute
for Space Research, which flew the AirSPEX instrument on board the ER-2 for the
second time. The instrument made its maiden flight on the ER-2 in January 2016.